diff --git a/drivers/pcf85063a/pcf85063a.cpp b/drivers/pcf85063a/pcf85063a.cpp
index 9312dba1..7e4599c0 100644
--- a/drivers/pcf85063a/pcf85063a.cpp
+++ b/drivers/pcf85063a/pcf85063a.cpp
@@ -137,11 +137,13 @@ namespace pimoroni {
 
   void PCF85063A::set_timer(uint8_t ticks, TimerTickPeriod ttp) {
     uint8_t bits = i2c->reg_read_uint8(address, Registers::TIMER_MODE);
-    // mask out timer tick period value and set new value
-    bits = (bits & ~0x18) | ttp;
-    // enable timer
-    bits |= 0x04;
-    i2c->reg_write_uint8(address, Registers::TIMER_MODE, bits);
+
+    uint8_t timer[2] = {
+      ticks,
+      uint8_t((bits & ~0x18) | ttp | 0x04) // mask out current ttp and set new + enable
+    };
+
+    i2c->write_bytes(address, Registers::TIMER_VALUE, timer, 2);
   }
 
   bool PCF85063A::read_timer_flag() {
diff --git a/drivers/pcf85063a/pcf85063a.hpp b/drivers/pcf85063a/pcf85063a.hpp
index 6c0fe037..5dd45c9c 100644
--- a/drivers/pcf85063a/pcf85063a.hpp
+++ b/drivers/pcf85063a/pcf85063a.hpp
@@ -38,10 +38,10 @@ namespace pimoroni {
     };
 
     enum TimerTickPeriod : int8_t {
-      TIMER_TICK_4096HZ       = 0,
-      TIMER_TICK_64HZ         = 1,
-      TIMER_TICK_1HZ          = 2,
-      TIMER_TICK_1_OVER_60HZ  = 3
+      TIMER_TICK_4096HZ       = 0b00 << 3,
+      TIMER_TICK_64HZ         = 0b01 << 3,
+      TIMER_TICK_1HZ          = 0b10 << 3,
+      TIMER_TICK_1_OVER_60HZ  = 0b11 << 3
     };
 
     //--------------------------------------------------
diff --git a/examples/pico_rtc/demo.cpp b/examples/pico_rtc/demo.cpp
index 1aaa7ad4..7ff5200f 100644
--- a/examples/pico_rtc/demo.cpp
+++ b/examples/pico_rtc/demo.cpp
@@ -93,8 +93,8 @@ int main() {
   printf("check timer function\n");
   printf("\n");
 
-  printf("- setting timer for in 3 seconds\n");
-  rtc.set_timer(3);
+  printf("- setting timer for in 5 seconds\n");
+  rtc.set_timer(5);
 
   printf("\n");
   printf("- waiting for timer flag\n");